This invention relates to basic refractory monoliths and, more particularly, it concerns a molybdenum trioxide bonded basic refractory and method.
Basic monoliths are refractory compositions which are either preformed or formed on site. They are installed by various forming techniques, such as casting, fettling, gunning, spraying, troweling, or in some cases by pressing. The term "basic" implies that the major component in the mix is a base oxide, such as lime, magnesia, or a combination of these common refractory oxides.
In the past, chromic acid (CrO.sub.3) has been the preferred binder for basic monoliths. Use of this binder imparted monolithic shapes with exceptional strength and slag resistance. Chromic acid contains the element chromium in the +6 valence state which is commonly referred to as hexavalent chrome.
While use of the chromic acid binder has provided adequate utility, recently, there has been a great deal of concern over the use of chromic acid because chromium +6 may be toxic and carcinogenic. For example, the EPA has forbidden routine disposal of materials containing more than 5 ppm of soluble chromium.
The refractory industry, in response to EPA concerns, has abandoned the use of chromic acid as a binder and has used as substitutes epsom (MgO.multidot.SO.sub.4 .multidot.7H.sub.2 O) salts, phosphates, silicates, nitre cake (NaH.multidot.SO.sub.4 .multidot.H.sub.2 O), sulfamic acid (H SO.sub.3 .multidot.NH.sub.2), citric acid, and anhydrous boric acid (H.sub.3 .multidot.BO.sub.3) either individually or in combination. Although these substitute binders have provided adequate service, they have not provided equivalent service to that achieved using chromic acid.
In light of the foregoing, there is a need for an improved basic refractory monolith including a binder which provides desired levels of slag resistance and strength and is environmentally safe.